首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 906 毫秒
1.
The effects of air movement upon sensible heat loss from individual birds at ambient temperatures of 20 degrees and 30 degrees C were determined by partitional calorimetry using a newly developed wind tunnel calorimeter. The relationship between area specific convective heat loss (W/m2) and air velocity (in the range 0.3 to 1.05 m/s) was described by y = 56.5 + 16.9 log x at an air temperature of 20 degrees C, but at 30 degrees C convective heat loss increased linearly with air speed (y = 11.8 + 40.1 x). At 20 degrees C sensible heat exchange (W/m2) was related to air velocity by y = 70.6 exp (0.099 x) and by y = 41.4 + 25.9 x at 30 degrees C, the proportional increase with air speed being greater at the higher temperature. The differences in the effects of air movement on convective cooling and sensible heat loss at 20 degrees and 30 degrees C reflect the thermoregulatory responses of the birds, induced by the thermal demands of the environment.  相似文献   

2.
1. The thermal preferences of small flocks of 400 chicks brooded under radiant heaters were determined at air temperatures of 21, 24 and 27 degrees C from observations of behavioural thermoregulation. 2. At 1 d of age the upper limits of the preferred black bulb temperature increased with air temperature. Preferences for radiant temperature declined with air temperature. 3. Compensation for cold air temperature was imperfect because the chicks avoided zones of high radiant flux. The maximum tolerable radiant temperature was approximately 50 degrees C. 4. Radiant heaters are preferable to convectors in poultry husbandry because the inherent lack of spatial homogeneity in thermal environments ensures that chicks can satisfy their individual thermal preferences.  相似文献   

3.
Energetics of sows and gilts in gestation crates in the cold   总被引：2，自引：0，他引：2  
Seventy pregnant sows and gilts in gestation crates with unbedded concrete-slat floors and partitions in common (which permitted contact by neighbors) in a closed house with air temperature 10 to 12 degrees C during cold weather were studied for 3 wk. The animals' lower critical temperature and thermoregulatory heat and feed requirements were estimated from measured variables, including ME intake, body weight and its change and body surface temperature, and other calculated values and assumptions. Estimates for a 165-kg sow or gilt in such an environment were: lower critical temperature = 15 degrees C; thermoregulatory heat requirement = 126 to 161 kcal/d per 1 C degree of coldness (higher as pregnancy progresses); and thermoregulatory feed requirement = 42 to 54 g/d per 1 C degree of coldness (assuming 3 kcal ME/g of diet). The sow's lower critical temperature was affected by state of pregnancy; in late pregnancy it was 1.6 to 2.6 C degrees lower than in early pregnancy. These estimates of the pregnant sow's thermoregulatory heat and feed requirements at effective environmental temperatures below the lower critical temperature accord well with those published before. But this estimate of the pregnant sow's lower critical temperature is approximately 5 C degrees lower than several made in laboratory settings on animals held individually, with no opportunity to huddle. The fact that every sow and gilt in this experiment could make mechanical contact with at least one neighbor at all times, and sometimes two, might account for much of the difference in lower critical temperature estimates.  相似文献   

4.
The activity of the ant Camponotus detritus was studied in the dunes of the central Namib Desert. Activity was divided into two components: transit activity and honeydew collection. Temperature governed both forms, but light controlled the initiation and termination of transit activity, which was bimodal in warm conditions and unimodal in cool conditions. No transit activity occurred at night. Ants were active over a surface temperature range of 10-55°C. Owing to a steep thermal gradient above the sand surface during the day in summer, the temperatures which the ants bodies experienced at 5 mm above the sand were 10-15°C lower than surface temperatures; well within the ants' physiological limits. Winds of about 16 km h-1 inhibited activity which ceased when wind speeds reached about 25 km h-1. In summer, the number of ants collecting honeydew was negatively correlated with air temperature while in winter it was positively correlated.  相似文献   

5.
1. The oxygen consumption and body temperature of White Leghorn x Rhode Island Red laying hens, which were being kept in a semi-natural climate, were periodically measured for short periods at ambient temperatures between 2 and 32 degrees C in a suitable chamber. 2. A seasonal shift was observed in lower critical temperature (Tc) and thermoneutral oxygen consumption. The slope of the relationship between oxygen consumption and air temperature at less than Tc was not discernibly affected by season. 3. The seasonal shifts correlated best with mean daily outside temperature Ta) during the experimental periods; a seasonal decrease of 10 degrees C in Ta was associated with a decrease of 8.5 degrees C in Tc and a 12% increase in thermoneutral oxygen consumption. 4. The capacity to maintain body temperature stability at extremes of environmental temperature was improved by acclimatisation to heat.  相似文献   

6.
The effect of body temperature (Tb) on the growth rate of male broilers was studied. Two pens (5 m2 each), one (A) near air inlets and one (B) near air outlets, were erected in a 12.5 m wide cross-ventilated, environmentally-controlled poultry house. Of 100 birds of both sexes in each pen, 18 males were marked and weighed weekly, and in three of these in each pen body temperature was measured by telemetry over 24 h at 50, 54, 55, 58, and 62 d of age. At 62 d group B birds weighed 250 g less than A; implanted birds weighed less than their group means, but relative growth rates were similar. Mean lowest (08.00 to 09.00 h) and highest Tb (11.00 to 17.00 h) in group A were 41.35 degrees C and 42.13 degrees C, and in group B 41.48 degrees C and 42.86 degrees C, respectively. The regression of G (percentage gain in body weight/d) on noon maximum Tb (Tbn) was G = 46.25 - 1.024 Tbn. This study suggests that an air temperature above 32 degrees C depresses body-weight gain of broilers by about 10% between 5 and 9 weeks of age. Therefore, house temperature should not be allowed to increase above 28 degrees C, except if relative humidity also increases to 0.70 or more.  相似文献   

7.
A report is given on an analysis of meteorological data on five locations in the region of Hessia in order to apply the BML's expert recommendation concerning ostrich farming. According to this recommendation black ice, very strong frost and continuous rain should not make it necessary to keep the animals in pens longer than 3 days or more often than 10 days per month. Otherwise a dry paddock must be provided. It was investigated whether and how often the above mentioned weather conditions exceeded the critical duration or frequency in the last decades at the different locations. Previously the weather related terms which were used in the BML-recommendation were defined more precisely in order to provide an objective basis for the analysis. Frequent periods of frost lasting longer than 3 days with temperatures below -5 degrees C were found to be a critical factor. They occurred in 79 to 90% of the winter seasons under investigation, although the climate was thought to be rather mild in comparison to other regions. Frost can not be remedied by a dry paddock. Therefore the locations in question are not suitable for ostrich farming. The same conclusion holds at least for all locations with a colder climate. Black ice occurred only scarcely. At none of the investigated locations periods of continuous rain were longer than 3 days or occurred more often than 10 days per month. This result might not only be due to the given climatic conditions but also due to methodological reasons. It seems that the meteorological definition of continuous rain is too restricted to take the relevant precipitation for ostriches into account. It is suggested to find a new definition and consider factors like humidity and wind speed as well.  相似文献   

8.
The influence of protein in exchange for carbohydrates on the energy maintenance requirement was studied with nearly fully-grown rats at ambient temperatures between 33 and 21 degrees C. The levels of the crude protein content were 10, 25, 40 and 70%. At an ambient temperature of 33 and 30 degrees C energy maintenance requirement increased with the growing protein content in the feed. At a temperature of 30 degrees C the following values of energy maintenance requirement were measured in the sequence of the protein levels mentioned: 330 +/- 11, 347 +/- 18, 360 +/- 15 and 399 +/- 15 kJ metabolizable energy/kg live weight 0.75 X d. The occurring changes largely coincide with the expected values calculated from the efficiency of the ATP synthesis in the oxidative catabolization of protein and carbohydrates. At ambient temperatures of less than 30 degrees C, thermogenous effects after the exchange of protein versus carbohydrates could only be observed partly or not. 30 degrees C in feeding on the maintenance level and 33 degrees C in the state of hunger are estimated as the lower critical temperatures. Below the critical temperatures down to 24 degrees C heat production increased less per 1 degree C temperature decrease both in hungry and fed rats than in the temperature range between 24 and 21 degrees C. By the decrease of the ambient temperature from 24 to 21 degrees C the heat production of the hungry or fed rats increased by 39 or 33 kJ/degrees C X kg live weight 0.75 X d.  相似文献   

9.
Outbreaks of epizootic hemorrhagic disease of deer and of bluetongue began in British Columbia in August and October 1987 respectively and recrudescence of infection by both viruses was detected the following year in August. Weather records for up to 18 days before the initial outbreaks of disease, isolation of virus or seroconversion were examined to determine if the viruses could have been introduced by infected Culicoides carried on the wind. Data on temperature, rainfall, wind speed and direction and pressure together with backward trajectory analysis showed that there were suitable winds which could have introduced Culicoides infected with epizootic hemorrhagic disease of deer virus on 13 August 1987 (14 days before disease was observed), Culicoides infected with bluetongue virus on 1 October 1987 (7 days before virus was isolated and 13 days before disease in sheep) and Culicoides infected with bluetongue or epizootic hemorrhagic disease of deer viruses on 20 July 1988 (15 days before seroconversion was detected). The arrival on 13 August 1987 coincided with the passage of a cold front and rain and that on 1 October 1987 with a fall in temperature and calm winds. The source of the Culicoides before arrival could have been the Okanogan Valley as far south as the junction of the Okanogan and Columbia rivers in Washington, USA. Flight would have been at temperatures of 12.6 degrees C or higher and at heights up to 1.5 km.  相似文献   

10.
Transport by road can induce significant stress in cattle. Thermal stress is among the main stress producing factors during transport. The provision of ventilation in livestock transport vehicles is usually through openings along the sides of the vehicle. The incoming air will affect air quality inside by regulating temperature, relative humidity, gas levels and levels of other contaminants. The aim of the present investigation was to map out the air quality in a commercial cattle transport vehicle under various climatic conditions and with varying stocking densities and transport times. Distributions of air temperature, relative humidity and concentrations of ammonia, carbon dioxide, oxygen and methane have been determined during 35 experimental journeys. In average the mean temperature inside the compartment was about 3 degrees C and 6 degrees C higher than outside temperature in summer (+7.8(-)+24.0 degrees C) and winter (-24.3(-)+12.7 degrees C) conditions respectively. The temperature increment inside, as could be expected from theory, increased with reduced ventilation and increased animal density. Many stops to load new animals lowered the temperature increment and relative humidity in winter time. In summer more stops made the compartment temperature and relative humidity increase. The inside temperature distribution was less than about 3 degrees C during both summer and winter season. Average ammonia level varied between 3 and 6 ppm depending on stocking density and number of stops with a maximum value of 18 ppm. No detectable methane levels could be found inside the compartment at any time.  相似文献   

11.
Two adult bottlenose dolphins (Tursiops truncatus) were individually housed in aboveground pools over a 10-day period and exposed to decreasing water temperatures to determine whether cold stress activated the hypothalamic-pituitary-adrenal axis. To serve as controls, two additional adult dolphins were similarly housed for the same duration but at ambient water temperatures (16.8-19.6 degrees C). Across all subjects, water temperatures ranged from 4.2 to 19.6 degrees C. Voluntary blood draws were made from each dolphin every 2-3 days, and serum was analyzed via radioimmunoassay for cortisol and aldosterone. Dolphins exposed to cold water showed an increase in serum cortisol and aldosterone as temperature declined; at the coldest water exposure, cortisol was more than three times and aldosterone more than two times the levels measured at ambient temperature. Elevations occurred before the water temperature declined below the individual animal's lower critical temperature, the point at which the metabolic rate increases to compensate for the loss of body heat. Variations in corticosteroids were unrelated to the 10-day isolation period, suggesting that the response was related to the cold stress and not impacted by the isolation. Elevations in cortisol and aldosterone were lower than those observed in force captured and stranded dolphins. Although potentially related to the general adaptive stress response, elevations in cortisol and aldosterone may have other adaptive functions related to mitigating impacts resulting from cold environmental temperatures.  相似文献   

12.
OBJECTIVE: To determine the critical temperature that reduces chondrocyte viability and evaluate the ability of chondrocytes to recover after exposure to the critical temperature. SAMPLE POPULATION: Cartilage explants obtained from the humeral heads of 30 sheep. PROCEDURES: In a randomized block design, 318 full-thickness cartilage explants were collected from 30 humeral heads of sheep and cultured for up to 14 days. On the first day of culture (day 0), explants were subjected to temperatures of 37 degrees , 45 degrees , 50 degrees , 55 degrees , 60 degrees , or 65 degrees C for 5 minutes by heating culture tubes in a warming block. The ability for chondrocytes to recover after exposure to the critical temperature was determined by evaluating viability at days 0, 1, 3, 7, and 14 days after heating. Images were analyzed by use of confocal laser microscopy. RESULTS: Analysis of images revealed a significant decrease in live cells and a significant increase in dead cells as temperature increased. Additionally, the deepest layer of cartilage had a significantly lower percentage of live cells, compared with values for the 3 most superficial layers. Chondrocytes did have some ability to recover temporarily after the initial thermal insult. CONCLUSIONS AND CLINICAL RELEVANCE: A strong relationship exists between increasing temperature and cell death, with a sharp increase in chondrocyte death between 50 degrees and 55 degrees C. Chondrocytes in the deepest cartilage layer are most susceptible to thermal injury. The threshold of chondrocyte recovery from thermal injury is much lower than temperatures reached during chondroplasty by use of most radiofrequency energy devices.  相似文献   

13.
178 Penicillium strains were isolated from moulded feedstuffs (mainly corn and wheat after ambient air drying, wheat after refrigeration, corn after treatment with propionic acid), and investigated for the effect of temperature on growth rate. Temperatures between 4 and 27 degrees C were used. 159 strains proved psychrotrophic, they were able to grow at 4 degrees C on malt extract agar (MA) as well as in wheat; the growth in wheat was indicated by the production of ergosterol. On MA all psychrotrophic strains were able to grow also at 10-27 degrees C. The maximum rate of growth was reached at 10-15 degrees C, 15-20 degrees C, 20-27 degrees C, or must be assumed for temperatures greater than or equal to 27 degrees C. At 4 and 10 degrees C the mean growth rate on MA was 24 and 51%, respectively, related to the mean rate at 20 degrees C; the lower temperature limit of growth was found at - 1 degree C by graphic extrapolation. The Q10 value of growth on MA is about 2, if temperatures between 20 and 10 degrees C are compared; with decreasing temperature higher Q10 values up to 3.7 are obtained. The growth rate of a strain of Penicillium aurantiogriseum on wheat was affected by temperature nearly in the same manner as on malt extract agar. The results are discussed with respect to the risk of moulding during refrigerated storage of feedstuffs.  相似文献   

14.
Forelimb surface temperatures were continuously monitored in four clinically normal ponies exposed to: (i) constant ambient temperature; (ii) a biphasic change in ambient temperature; and (iii) an incremental increase in ambient temperature. Limb surface temperatures were recorded at the hoof, metacarpus and forearm, and rectal temperature was also measured. Under constant ambient temperature, limb surface temperatures remained relatively constant. A pyrexic episode occurred in one pony under constant ambient temperature conditions and was characterised by an onset phase in which rectal temperature gradually increased while limb surface temperatures concurrently decreased; a plateau phase in which rectal temperature was elevated but essentially constant although limb surface temperatures rose dramatically; and a febrilytic phase in which limb surface temperatures remained elevated while rectal temperature gradually decreased. A biphasic change in ambient temperature produced corresponding changes in limb surface temperature, but limb surface temperatures were less stable at the lower ambient temperatures. Surface temperature responses to incremental increases in ambient temperature were dependent on the baseline ambient temperature (before increase), and dramatic, spontaneous increases in limb surface temperatures were observed. Rectal temperatures in the normal animals remained relatively constant under all three ambient temperature regimens. It was concluded that clinical interpretation of limb surface temperatures in ponies required an awareness of ambient temperature conditions. For evaluation of vasodilator agents, constant ambient temperatures of at least less than 18 degrees C are suggested, and constant ambient temperatures exceeding 20 degrees C are recommended for the evaluation of vasoconstrictor agents.  相似文献   

15.
A thermal analgesiometric device was developed for unrestrained cats. Heat was provided by an electrical element potted together with a temperature sensor in thermally conductive epoxy in a 5 gm probe. This was attached to an elasticated band round the cat's thorax with an inflated bladder maintaining constant pressure between probe and skin. A safety cut-off was set at 60 degrees C. End point was a skin flick, turning, or jumping. Threshold temperatures in untreated cats were around 40 degrees C and repeatable to 4 degrees C with 5, 10 or 15 minutes between tests. Threshold temperature was stable in tests at 15 minutes intervals without false positives or negatives. Tests repeated at weekly intervals were repeatable to within 4 degrees C. Treatment with the opioid analgesic pethidine increased the threshold temperatures 10.2 (6.7) degrees C 45 minutes after treatment. The device was well tolerated for at least 24 hours and the analgesic effect of an opioid was detected. The system appears suitable for use in investigations into analgesic pharmacology in cats.  相似文献   

16.
Estimates of heat stress relief needs for Holstein dairy cows   总被引：3，自引：0，他引：3  
Estimates of environmental heat stress are required for heat stress relief measures in cattle. Heat stress is commonly assessed by the temperature-humidity index (THI), the sum of dry and wet bulb temperatures. The THI does not include an interaction between temperature and humidity, although evaporative heat loss increases with rising air temperature. Coat, air velocity, and radiation effects also are not accounted for in the THI. The Holstein dairy cow is the primary target of heat stress relief, followed by feedlot cattle. Heat stress may be estimated for a variety of conditions by thermal balance models. The models consist of animal-specific data (BW, metabolic heat production, tissue and coat insulation, skin water loss, coat depth, and minimal and maximal tidal volumes) and of general heat exchange equations. A thermal balance simulation model was modified to adapt it for Holstein cows by using Holstein data for the animal characteristics in the model, and was validated by comparing its outputs to experimental data. Model outputs include radiant, convective, skin evaporative, respiratory heat loss and rate of change of body temperature. Effects of milk production (35 and 45 kg/d), hair coat depth (3 and 6 mm), air temperature (20 to 45 degrees C), air velocity (0.2 to 2.0 m/s), air humidity (0.8 to 3.9 kPa), and exposed body surface (100, 75, and 50%) on thermal balance outputs were examined. Environmental conditions at which respiratory heat loss attained approximately 50% of its maximal value were defined as thresholds for intermediate heat stress. Air velocity increased and humidity significantly decreased threshold temperatures, particularly at higher coat depth. The effect of air velocity was amplified at high humidity. Increasing milk production from 35 to 45 kg/d decreased threshold temperature by 5 degrees C. In the lying cow, the lower air velocity in the proximity of body surface and the smaller exposed surface markedly decrease threshold temperature. The large variation in thresholds due to environmental and animal factors justifies the use of thermal balance-based indices for estimating heat stress. Such an approach may make possible estimates of threshold temperatures at which heat stress relief is required for widely different cattle types and environmental situations.  相似文献   

17.
The aim of this study was to determine the trapping efficacy of Duddingtonia flagrans against Haemonchus contortus at the temperature ranges experienced around lambing in the major sheep producing regions of Australia. Faeces were collected from Merino wethers, maintained in an animal house and which had received either D. flagrans chlamydospores for a 6-day period (DF) or not (NIL). Faeces were incubated at one of four daily temperature regimens which were composed of hourly steps to provide 6-19 degrees C, 9-25 degrees C, 14-34 degrees C and 14-39 degrees C to mimic normal diurnal air temperature variation. Enumeration of the number of preinfective and infective larvae that had migrated from or remained in faecal pellets was used to calculate percentage recovery and trapping efficacy of D. flagrans. Recovery of H. contortus larvae of both stages was significantly lower in DF faeces but the magnitude of the effect was considerably greater for infective larvae. Mean recovery of infective larvae from NIL and DF faeces was 10.6 and 0.4%, respectively, indicating a mean trapping efficacy of 96.4%. The lowest trapping efficacy (80.7%) was observed at 6-19 degrees C but total recovery of infective larvae, from DF faeces, was greatest at the two highest temperature regimens, although still less than 0.9%. The results of this study indicate that typical Australian lambing temperatures should not be a barrier to the use of D. flagrans as an effective biocontrol of H. contortus in Australia.  相似文献   

18.
1. Two experiments are described in which laying pullets maintained at constant temperatures were fed a range of diets with a view to defining optimum combinations of temperature and nutrient intake. 2. In the first experiment, all combinations of 6 temperatures (15 degrees, 18 degrees, 21 degrees, 24 degrees, 27 degrees and 30 degrees C) 9 diets (three protein concentrations and three energy contents) and two stocks were tested for 34 weeks using 4320 pullets. In experiment 2, all combinations of three rearing temperatures, three laying temperatures (18 degrees, 22.5 degrees and 27 degrees C) three diets (protein concentration) and two stocks were tested for 61 weeks using 2160 pullets. 3. As anticipated, higher dietary protein concentrations were needed to maintain egg output at higher temperatures. If diets suplying adequate amino acid intakes were provided, egg output was unaffected by temperatures in the range 15 degrees to 27 degrees C although, at the highest temperature, egg weight was slightly reduced and rate of lay (particularly in the later part of the laying year) was increased. At 30 degrees C, egg output was depressed whichever diet was fed. 4. Dietary energy content had small but significant effects on egg weight and egg output but did not interact with temperature. It was not possible to maintain egg weight or egg output at 30 degrees C by feeding a high energy, high protein diet. 5. Estimated heat output of the birds increased during the course of the experiment at the lower temperatures but decreased with time at 30 degrees C. Feather loss occurred earlier at the lower temperatures and this is interpreted as an effect of temperature on the timing of the annual moult, which also accounts for the better persistency of lay observed at 27 degrees C.  相似文献   

19.
Environmental factors were evaluated to determine potential limitations in using cattle eye temperatures obtained through infrared thermography (IRT) for early disease detection systems or in animal welfare research studies. The effects of the following factors on IRT eye temperatures in cattle and a fabricated surrogate “eye” were evaluated: camera to object distance, wind speed, camera settings (distance, emissivity, and humidity), and solar loading. Wind speed in both live animals and using a surrogate “eye” was found to decrease the IRT temperature. In the presence of ∼7 km/h wind, the mean IRT eye temperature decreased by 0.43 ± 0.13 °C and; at higher wind speeds (∼12 km/h), the temperature decreased by 0.78 ± 0.33 °C. Direct sunlight was found to increase the IRT eye temperature by 0.56 ± 0.36 °C. It was determined that environmental factors impact IRT temperature measurements significantly and therefore must be managed to ensure reproducible and accurate readings.  相似文献   

20.
The thermal environment comprises factors which influence an animal's heat exchange through the channels of evaporation, radiation, convection and conduction. The air temperature is often used by itself as an assessment of the thermal environment, but air temperature by itself is inadequate for this purpose unless conditions are standardized with air and mean radiant temperatures equal to each other, free convection, and an insulated floor. Farming environments are not standardized, but climatic investigations allow an equivalent standardized environmental temperature (ESET) to be calculated for a given situation.Information on energy retention and heat loss in the pig has been derived from experiments under standardized conditions. ESET can be used to transfer the results of these experiments to pig farming conditions, and to determine for different types of housing the air temperatures equivalent to the effective critical temperatures found under standardized conditions.Experimental results can then be used to estimate the production losses which occur when ESET falls below the critical temperature, and the decision can be taken on increasing feed or improving heating or nsulation. For pigs in gorups in the body weight range 20–50 kg, the calculated air temperatures for maximum productivity range from 14°C in an insulated house free from draughts to 22°C in an uninsulated house with draughts in winter. Below these temperatures the animals' heat losses increase by approximately 4 kJ/°C per kg per day. For a feed with 1 g  12 kJ metabolizable energy, the increased heat loss leads to an increased feed requirement of 0.3 g/°C per kg per day for maintaining maximum production.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号